The present invention relates generally to the field of disc drive data storage devices, and more particularly, but not by way of limitation, to an automated assembly of a disc drive head-disc assembly which includes an automated clampring installation station.
Modern hard disc drives are commonly used in a multitude of computer environments, ranging from super computers through notebook computers, to store large amounts of data in a form that can be made readily available to a user. Typically, a disc drive comprises one or more magnetic discs that are rotated by a spindle motor at a constant high speed. The surface of each disc is a data recording surface divided into a series of generally concentric recording tracks radially spaced across a band having an inner diameter and an outer diameter. Extending around the discs, the data tracks store data within the radial extent of the tracks on the disc surfaces in the form of magnetic flux transitions induced by an array of transducers, otherwise commonly called read/write heads. Typically, each data track is divided into a number of data sectors that store fixed sized data blocks.
The read/write head includes an interactive element such as a magnetic transducer which senses the magnetic transitions on a selected data track to read the data stored on the track. Alternatively, the read/write head transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the track.
As is known in the art, each read/write head is mounted to a rotary actuator arm and is selectively positionable by the actuator arm over a selected data track of the disc to either read data from or write data to the selected data track. The read/write head includes a slider assembly having an air-bearing surface that causes the read/write head to fly above the disc surface. The air bearing is developed as a result of load forces applied to the read/write head by a load arm interacting with air currents that are produced by rotation of the disc.
Typically, a plurality of open-center discs and open-centered spacer rings are alternately stacked on the hub of a spindle motor, followed by the attachment of a clampring to form a disc pack. The hub, defining the core of the stack, serves to align the discs and spacer rings around a common centerline. Movement of the discs and spacer rings is typically constrained by a compressive load maintained by the clampring. The read/write heads mounted on a complementary stack of actuator arms, which compose an actuator assembly, commonly called an xe2x80x9cE-block,xe2x80x9d accesses the surfaces of the stacked discs of the disc pack. The E-block also generally includes read/write head wires which conduct electrical signals from the read/write heads to a flex circuit which, in turn, conducts the electrical signals to a printed circuit board assembly (PCB). When the E-block is merged with the disc pack into a base deck and a cover is attached to the base deck a head-disc assembly (HDA) is formed. For a general discussion of E-block assembly techniques, see U.S. Pat. No. 5,404,636 issued to Stefansky et al., assigned to the assignee of the present invention.
The head-disc assembly (HDA) of a disc drive is typically assembled in a clean room environment. The need for maintaining a clean room environment (free of contaminants of 0.3 micron and larger) is to ensure the head-disc interface remains unencumbered and damage free. The slightest damage to the surface of a disc or read/write head can result in a catastrophic failure of the disc drive. The primary causes of catastrophic failure, particularly read/write head crashes (a non-recoverable, catastrophic failure of the disc drive) are generally characterized as contamination, exposure to mechanically induced shock, and non-shock induced damage. The source of non-shock induced damage is typically traced to the assembly process, and generally stems from handling damage sustained by the disc drive during the assembly process.
Several factors that bear particularly on the problem of assembly process induced damage are the physical size of the disc drive, the spacing of the components, the recording densities sought to be achieved and the level of precision to be maintained during the assembly process. The high levels of precision required in all of the assembly process are necessary to attain the operational tolerances required by the disc drive. The rigorous operational tolerances are in response to market demands that have driven the need to decrease the physical size of disc drive while simultaneously increasing disc drive storage capacity and performance characteristics.
Demands on disc drive mechanical components and assembly procedures have become increasingly more critical in order to support capability and size in the face of these new market demands. Part-to-part variation in critical functional attributes in the magnitude of a micro-inch can result in disc drive failures. Additionally, as disc drive designs continue to decrease in size, smaller read/write heads, thinner substrates, longer and thinner actuator arms, and thinner gimbal assemblies will continue to be incorporated into the drives, significantly increasing the need to improve the assembly processes to protect the read/write heads and discs from damage resulting from incidental contact between mating components. The aforementioned factors resultantly increase the difficulty of assembling disc drives. As the assembly process becomes more difficult, the need to invent new tools, methods, and control systems to deal with the emerging complexities pose unique problems in need of solutions.
Coupled with the size and performance improvement demands are further, market driven requirements for ever-increasing fault free performance. The progression of continually decreasing disc thickness and disc spacing, together with increasing track density and increasing numbers of discs in the disc pack, has resulted in a demand for tools, methods and control systems of ever increasing sophistication. A result of the growth in demand for sophisticated assembling equipment has been a decreasing number of assembly tasks involving direct operator intervention. Many of the tasks involved in modem methods are beyond the capability of operators to reliably and repeatedly perform, further driving the need for automation equipment and tools.
In addition to the difficulties faced in assembling modem disc drives of high capacity and complex, physical product performance requirements have dictated the need to develop new process technologies to ensure compliance with operating specifications. The primary factor driving more stringent demands on the mechanical components and the assembly process are the continually increasing areal densities and data transfer rates of the disc drives.
The continuing trend in the disc drive industry is to develop products with ever increasing areal densities, decreasing access times and increasing rotational speeds. The combination of these factors places greater demands on the ability of modern servo systems to control the position of read/write heads relative to data tracks. The ability to assemble HDA nominally free from the effects caused by unequal load forces on the read/write heads, disc pack imbalance or one of the components of runout, velocity and acceleration (commonly referred to as RVA) posses a significant challenge as track densities increase. The components of RVA are: disc runout (a measure of the motion of the disc along the longitudinal axis of the motor as it rotates); velocity (a measure of variations in linear speed of the disc pack across the surface of the disc); and acceleration (a measure of the relative flatness of the discs in the disc pack).
By design, a disc drive typically has a discreet threshold level of resistance to withstand rotationally induced noise and instability, below which the servo system is not impaired. Also, a fixed range of load forces must be maintained on the read/write head to ensure proper fly height for data exchange. The primary manifestations of mechanically induced noise and instability are (1) vibration induced read/write head oscillation, (2) beat frequencies written into the servo signal at the servo write station and (3) non-repeatable runout. Oscillations are often introduced to the system via (1) deformations of the disc surface, (2) harmonics induced by disc pack imbalance, or (3) excessive surface accelerations encountered by the read/write head while flying on track or traversing the disc surface during track seeks.
Verification of disc pack compliance to the RVA specifications is crucial to the overall quality and long term reliability of the product. To ensure RVA compliance, measurements are taken to determine: (1) the amount of runout present in the disc pack, (2) absence of concave or convex disc profile as well as absence of a wavy disc profile across the surface of the discs, and (3) absence of a wavy disc profile around each track circumference.
The foregoing measurements require sophisticated measurement instruments and techniques. The complexities of the measurements render such measurements very difficult for an operator to perform, particularly at high assembly run rates. Specific problems arising out of operator executed or operator-assisted measurements include the frequency of damage to the discs and inconsistent and/or inaccurate measurement results obtained from a manually based measurement process. Both component damage and measurement errors occur from operator inability to maintain a sufficiently close interface with the measurement instruments as is demanded by the measurement process and associated instruments.
The operating performance of the disc drive servo system is affected by mechanical factors beyond the effects of mechanically induced read/write head oscillation from disc surface anomalies. Errors are traceable to disc pack imbalance and RVA noise sources. Even with improved approaches to the generation of position error signals in the disc drive servo system, the ability of the system to deal with such issues is finite. The limits of the servo system capability to reliably control the position of the read/write head relative to the data track must not be consumed by the noise present in the HDA resulting from the assembly process. Consumption of the available margin by the assembly process leaves no margin in the system to accommodate changes in the disc drive attributes over the life of the product. An inability to accommodate changes in the disc drive attributes leads to field failures and an overall loss in product reliability, a detrimental impact to product market position.
Although the servo system is that primarily affected by mechanically induced system noise, the disc drive read-write channel is equally dependent upon the mechanical integrity of the HDA. Issues regarding the inability of an oscillating read/write head to accurately read servo data also apply to read-write data. However, it is typical for read-write data to demonstrate a much lower signal to noise ratio than is present in the disc drive servo burst signals and gray code, thereby rendering read/write head capability in read data fields more susceptible to read errors. Read errors have frequently been traced to head-disc misalignments of the type causing a change in the fly height characteristics of the read/write head. Changes in fly height that increase the fly height cause the read/write head transducer to be located farther away from the data fields. The increased distance between the transducer and the data field imparts the perception of a decrease in data bit field strength relative to the background noise, resulting in an inability to read the data contained in the data field. Attempts to perform accurate measurements of head-disc misaligments, occurring as a result of disc pack tilt, have not been successful in manual head-disc merge operations. The inability to verify the presence of a head-disc misalignment during the read/write head-disc merge operation leads to rework of disc drives that subsequently fail in the disc drive production process. Reworking of disc drives exposes the disc drive, in particular the HDA, to increased handling, thereby increasing the probability of damage to the disc drive.
Components of modern disc drives have a relatively high susceptibility to damage induced through mechanical shock. One type of shock induced damage presented by prior merge operations deals with the problem of xe2x80x9chead slap.xe2x80x9d Head slap is a term used to describe the dynamics of a read/write head, resting on a disc, in response to mechanically induced shock. The shock causes the read/write head to lift off the disc, and once off the disc the gimbal spring cants the read/write head as the force of the load arm drives the read/write head back to the disc. Typically, the first point of contact of the read/write head with a disc occurs that the owners of the read/write head. It is known that shocks of a load of greater than 20 grams for duration of 0.5 milliseconds or less will cause head slaps. It is also well known that the results of head slap often lead to read/write head crashes.
Taken in combination the above discussed factorsxe2x80x94the tasks involved in assembling a modern disc drive exceeds the capability of manual assemblers; the susceptibility of the disc drive to damage during the assembly process; the level of precision assembly required by increasing areal densities; and the need to minimize adverse effects of mechanically induced noise on the disc drive servo systemxe2x80x94have culminated to render prior disc drive assembly method archaic.
Thus, in general, there is a need for an improved approach to disc drive assembling technology, to minimize the potential of damage during assembly, to produce product that is design compliant and reliable, and to minimize mechanically induced system noise. More particularly, there is a need for an automated clampring installation station for installation of a clampring on a disc pack of a disc drive.
The present invention provides an automated clampring installation station for installing a component on a disc drive by picking, placing and attaching a component, for example a clampring, on a workpiece, for example a disc pack mounted in a base deck, by use of hardware, for example screws, during an automated assembly process. Included in the automated clampring installation station and attached to a frame are five major assemblies working in conjunction to achieve the assembly task assigned the automated assembly disc drive assembly station.
The first of the five major assemblies is a control computer that orchestrates the activities of the remaining four major assemblies. The second major assembly is a conveyor that responds to a workpiece delivery command from the control computer by delivering a hub and interleaved member parts into the automated clampring installation station. Once the hub and interleaved member parts is registered within a predetermined component attachment location within the station, the station control station commands the second major assembly, a hardware dispensing assembly to activate.
The hardware dispensing assembly responds to a command from the control computer by activating its hardware dispensing routine. Having activated the routine the hardware dispensing assembly automatically stags a predetermined required quantity of hardware, such as screws, in a predetermined geometric configuration within fixed hardware pick-up location to await pick-up and then self deactivates.
The third major assembly, a presentment assembly, is activated in conjunction with the hardware dispensing system by an activation command from control computer. The presentment assembly responds to a command from the control computer by activating its component parts feeding routine. Having activated the routine the presentment assembly automatically delivers a component, such as a clampring, to a predetermined awaiting pick-up location and then deactivates itself.
The fourth major assembly, a positioning and attachment assembly has two primary portions. A transport and affixing assembly and a feature detection assembly. The transport and affixing assembly responds to a hardware pick-up command from the control computer by moving to the transport and affixing assembly and picking up the hardware, for example six screws. As both the transport and affixing assembly and the feature detection assembly are attached to the same linear positioning arm they move in unison. Such that, while picking up the hardware, a digital video camera component of the feature detection assembly is automatically positioned above the predetermined awaiting pick-up location to analyzes the features of the component.
Having picked up the hardware, the component and hardware transport and affixing is repositioned above the predetermined awaiting pick-up location and then re-oriented to be in alignment with the component. The amount of re-orientation needed is based on the analysis of the component""s features that were captured by the feature detection assembly. Having come into alignment, a command is issued by the control computer to pick up the component, such as the clampring. During pick-up of the component, the digital video camera component of the feature detection assembly automatically analyzes the features of the hub and interleaved member parts or disc pack.
Having picked up both the hardware and the component, the control computer commands the positioning and attachment assembly to first, move the component and hardware transport and affixing above the hub and interleaved member parts; second, orient the hardware and the component to be in alignment with the hub and interleaved member parts; and third, attach the component to the hub and interleaved member parts using the hardware. Upon completion and receipt of a release command from a conveyor control station, the control computer commands the release of the disc pack to the conveyor and issues a delivery command to the conveyor to deliver a new hub and interleaved member parts to the automated clampring installation station.
A benefit imparted to the disc drive by the automated clampring installation station is the minimization of two components of RVA. First, the minimization of encountering concave or convex disc profile or wavy disc profile across the surface of the discs and second, the minimization of encountering a wavy disc profile around each track circumference. The minimization of two of the three components of RVA results from the ability of the automated clampring installation station to simultaneously torque down the attachment screws.